look on wikipedia.org, it shows a description of it~
Queen mab was mention by Mercutio in scene vi, who was mocking about Romeo's believe in dreams.
Romeo and Juliet actually both had moustaches, however Romeo had two.
Queen Mab was a fairy in romeo and Juliet who helped them
Romeo and Juliet look like the actor and actress who play the parts in whatever production you are watching. Shakespeare did not give descriptions of them.
She doesn't have a described appearance